1,721,007 research outputs found
THE ROTATION OF LAGEOS
No full textIn view of the need of an accurate modelling of nongravitational forces on laser-tracked satellites, it is important to understand their rotational dynamics, which determines the temperature anisotropy and the ensuing radiation recoil effects. We propose a model of the torques acting on LAGEOS due to eddy currents and gravity gradient. The electromotive forces induced in the spacecraft by its rotation in the magnetic field of the Earth dissipate angular momentum and produce a precession of the spin axis; the oblate spacecraft will precess in the gravitational field of the Earth at a rate proportional to the rotation period. Therefore the gravitational torques become more and more important with time and eventually may produce a chaotic dynamics. The predicted evolution of the spin period agrees very well with the few experimental data available and corresponds to an approximately exponential growth rate of about 3 years
Modern Cosmology in retrospect, ed. by B. Bertotti, R. Balbinot, S. Bergia, A. Messina (Cambridge : Cambridge Univ. Press., 1990)
No full textModern Cosmology in retrospect, ed. by B. Bertotti, R. Balbinot, S. Bergia, A. Messina (Cambridge : Cambridge Univ. Press., 1990). In: Revue d'histoire des sciences, tome 45, n°1, 1992. p. 153
Modern Cosmology in retrospect, ed. by B. Bertotti, R. Balbinot, S. Bergia, A. Messina (Cambridge : Cambridge Univ. Press., 1990)
No full textModern Cosmology in retrospect, ed. by B. Bertotti, R. Balbinot, S. Bergia, A. Messina (Cambridge : Cambridge Univ. Press., 1990). In: Revue d'histoire des sciences, tome 45, n°1, 1992. p. 153
Plasma effects on Doppler measurements of interplanetary spacecraft. I - Discontinuities and waves
No full textThe authors present an analysis of effects of plasma turbulence in the solar wind on Doppler radio measurements from interplanetary spacecraft. In particular, with respect to previous work, the authors introduce physically different components of the fluctuations, e.g. discontinuities and waves in the study of variations of radio fluctuations with elongation angle. They show, correspondingly, that there is a critical angle, near maximum elongation, where the phase fluctuations of the radio waves are dominated by waves and not discontinuities. The analysis leads also to a better determination of the minimum noise level coming from plasma fluctuations and is therefore important from the point of view of gravity wave detection using Doppler techniques
The effect of the motion of the Sun on the light-time in interplanetary relativity experiments
No full textIn 2002, a measurement of the effect of solar gravity upon the phase of coherent microwave beams passing near the Sun was carried out by the Cassini mission, allowing a very accurate measurement of the PPN parameter γ. The data have been analysed with NASA's Orbit Determination Program (ODP) in the Barycentric Celestial Reference System, in which the Sun moves around the centre of mass of the solar system with a velocity v⊙ of about 15 m s-1; the question arises: what correction does this imply for the predicted phase shift? After a review of the way the ODP works, we set the problem in the framework of Lorentz (and Galilean) transformations and evaluate the correction; it is several orders of the magnitude below our experimental accuracy. We also discuss a recent paper (Kopeikin et al 2007 Phys. Lett. A 367 276), which claims wrong and much larger corrections, and clarify the reasons for the discrepancy. © 2008 IOP Publishing Ltd
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